Search

Cordierite-acicular mullite composites containing 0, 25, 50, 75 and 100 wt% of mullite were fabricated from waste MoSi 2 and commercial powders of Al 2 O 3 and spinel (MgAl 2 O 4). Careful oxidation of pulverised waste MoSi 2 rendered a precursor mixture of MoO 3 and amorphous SiO 2 , which served as pore forming agent and SiO 2 source, respectively. Evaporation of MoO 3 at ∼750 °C allowed production of highly porous cordierite-mullite ceramic composite after sintering in air at 1350 °C for 4 h. The combination of equiaxed cordierite grains and elongated (prism-like) mullite grains, resulted in unique microstructure with open porosity between 53.3 and 55.6 vol% which makes the obtained composite convenient for application as diesel particulate filter material. The presence of mullite affected four key thermo-mechanical properties which determine the thermal shock resistance of cordierite-mullite composite. The best thermal shock resistance was measured in composite containing 75 wt% of mullite. It was a result of improved thermal conductivity (1.081 W/mK) and bending strength (3.62 MPa) and relatively low values of coefficient of thermal expansion (3.8 × 10−6 K−1) and elastic modulus (2.27 GPa). [ABSTRACT FROM AUTHOR]

Comprehensive study on effect of YAG amount on densification, creep resistance and room-temperature mechanical properties of Al 2 O 3 -YAG composite pressureless sintered at 1600 °C was conducted. The main goal was to optimize the amount of YAG in order to fabricate a composite with improved creep resistance and sufficiently good room-temperature mechanical properties. The composite was made by mixing a commercially available Al 2 O 3 powder with fine YAG powder obtained by glycine-nitrate combustion synthesis starting from aluminum nitrate and yttrium nitrate. Increased driving force for sintering of fine YAG powder allowed fabrication of dense Al 2 O 3 -YAG composite with up to 30 vol% YAG. The presence of YAG was found to be very effective in improving creep resistance of Al 2 O 3 -YAG composite. Large Y3+ ions blocked diffusion along Al 2 O 3 grain boundaries, reduced diffusivity and therefore enhanced creep resistance of Al 2 O 3 -YAG composite which continuously increased as the YAG amount increased. Тhe presence of YAG was also found to improve mechanical properties such as hardness and elastic modulus. The improvement of these properties was ascribed to increased density of Al 2 O 3 -YAG composites owing to high sintering activity of YAG powder. While fracture strength of the composite can be as high as that of monolithic Al 2 O 3 , fracture toughness of composite decreased continuously as the YAG content increased. The decrease was ascribed to transgranular fracture of both YAG and Al 2 O 3 grains in samples containing larger amounts of YAG. The proper balance between fracture toughness and creep resistance was found in composite containing 18 vol% YAG which had considerably improved creep resistance accompanied by a relatively small decrease in fracture toughness. [ABSTRACT FROM AUTHOR]